Noise discriminating system



July 14, 1953 H. F. OLSON ET AL 2,645,684

NOISE DISCRIMINATING SYSTEM Filed June 30, 1948 INVENTORSI hAnnv F. DLSDN & I HN PRE//STDN BY ATTO'RNEY "needles,.loudspeakers, and the like.

frequencies Patented July 14,Y 1953 NOISE DIS CRIMINATING SYSTEM Harry F. Olson, Princeton, and John Preston,

Metedeconk, N. J., assignors to Radio Corporation of America,` a corporation of Delaware Application June 30, 1948, Serial No. 36,197

16 Claims.

. 'Ifhisinventionrelates to sound translating de- `vices',`andfmo re particularly to a mechanical system for discriminating against noise or other undesirable signals in sound translating devices. "Interference from noise, particularly in the high frequency range, has always been a problem insoundtranslating devices such as phonograph High frequency noise `is,`in general, more disagreeable than low frequency noise. `The level of the noise isv usually much lower than the average useful signal level. In order to discriminate against high frequency noise in sound translate ing devices, it is necessary to eliminate or separate thefinput of noise signal from that of the useful signal prior to reproduction.

The primary purpose of ourpresent invention,

therefore, is to eliminate orreduce interference lfrom noise in sound translating devices.

` It is also an object of our invention to provide a system which will discriminate against high frequency signals of low amplitude.

It is another object of.our invention to provide a system for sound translating devices wherebynoise in thehigh frequency range and up to va predetermined level will not be reproduced but` the useful signal above said noise llevel will be reproduced.

Interference from noise can, as a general rule, be eliminated or reduced by limiting. This is customarily `accomplished by providing linear corrugations or compliances `between the driving member or driving force andthe translating 'member which transforms the mechanical vibrations into acoustical vibrations. These ,corrugations orcompliances tend tosmooth out the middle register of frequencies and attenuate or hold down the extreme high frequencies, the low being comparatively unaffected. However, this system is found to discriminate Iagainst useful signals as well as undesirable signals above a certain range offrequencies.

In accordance with our present invention, we provide a system for ltering out undesirable high frequency signals below a predetermined amplitude whereby high frequency noise below this level will be eliminated or reduced, and the useful signal above this noise level will be reproduced. In order to accomplish this, we pro- Y vide a compliantcoupling between the driving member and the translating member, the coupling comprising a pair of compliances disposed 1 in l seriesirelation for linear driving movement.

"The function of these compliances is to filter out `signals abovea predetermined range of frequencies and below a given amplitude.'l For cooperation with the initial compliance adjacent the driving member, we provide a non-linear driving element. The non-linear driving element bridges the initial compliance and is arranged to transmit high frequency signals above a predetermined amplitude directly to the second compliance adjacent the translating member, while the initial compliance filters out the undesirable high frequency signals Vbelow that I input-output amplitude characteristic of the vyi-` brating system illustrated in Fig. l,

Fig. 3 is a curve representing the Ihigh frequency input-output amplitudecharacteristic of the vibrating system illustrated in Fig. 1,

Fig. 4 shows curves representing the output response-frequency characteristics for equal increments of input in the vibrating system shown in Fig. 1,

Fig. 5 shows curves representing high frequency noise input and output in the vibrating system illustrated in Fig. 1,

Fig. 6 shows curves representing high frequency signal input and output in the vibrating systeml illustrated in Fig. 1,

Fig. '7 is a sectional View of the vibrating sysf tem of a dynamic loudspeaker in accordance with our winvention, .i

Fig. 8 isa front View of a phonograph needle ,in accordance with our invention, Y

Fig. 9 is a side view of the phonograph` needle illustrated in Fig. 8,

Fig. 10 is a front view, partly in section, of a modied form of 1 phonograph needle constructed in accordance with our invention, and

Fig. 11 is an enlarged, fragmentary View showing a portion of the loudspeaker of Fig. 7.

Referring more particularly to Fig. 1 ofthe drawing, there is shown an initial or first compliance C1l connected in series withl a second compliance C2 by a mass M for linearly transmite ting signals of predetermined frequency and amplitude.` The degree of impedance provided by these compliances determines their output of frequency' and amplitude. `If `the impedance is l amplitude.

asuseiul high frequency signals below a certain undesirable noise signals, We have provided an intermediate non-linear driving elementor member D vvlii'cll bridges the initial ccmpliance adjacent the input driving member iyhichA is responsive to predetermined movements of the irl'-l put driving member. The non-linear driving member Dis substantially rigid andl hasV one of its ends freely suspended between a pair of stops S on the mass M spacedA al-[predetermined distance for limiting the Oeffectilfe' "co pliance of the initial compliance Ci. VThe 'cliarl acteristics of the system are suchv that, inpracftice, when low frequency signals are impartedto the system, Vthe mechanical impedance of the compliance Cris large compared to the mechanical iinpedance of the mass M and the load Z. Under these conditions, the inputoutput char'- acteristic, as s'hovvn by Fig. 2*, is linear since the non-linear element does not influence` the performance. Signal inputs of high frequency, however', result in little or no output of those signals in the absence of the nonfli'nea'r elenient since, ,at the higher frequencies; the mechanical impedance of the compliance 'C11A is s'inall compared to the mechanical impedance ofthe mass M and the load Z. d If the hon-linear iiienilocr D is iid-ooo, there is vrylitile high frequency output until the signal amplitude reaches a predetermined value determined by the spacinfg betv'veen the freely suspended en'dyIEl lof the member D and the stops S. Any high frequency signals greater than this predetermined amplit'ude would cause the free end E 'of the non-linear driving member to strike the stops S- which are spaced apart in accordance iii/ith the amplitude of the useful signals'to b'e reproduced. Thus. for selected signals, the 'non-'linear drivingV niember selectively shunts the compliance C1.` The inputoutp'ut Vcharacte'ristic is then linear, as shown by thecurv'e in Fig. '3.

The effectiveness of the vnon-linear driving r'r'l'ernber Das a noi's'e discriminator isals'o sh'ovvn the 'curves in 4 of the drawing. Ifh'ese curves represent the response-frequency char'- aIc'ter'isti'cs forr'eqlial increments o'f-in-p'ut for a 'sound translating dev'ice constructed in "accordance with our invention. It VWill be seen, in Fig. 4, thajtthere is a very high discrimination against h'igh frequencies` having, smallA input. However, for high frequencies of larger ,input there is no discrimination. The advantage of using a nonlinear Adlf'vilig'eler'n'ent in the vbratory systen Vis also shown by the curves! illustrated in VFigs/ aride which show inputand output characteristics for high frequency noise and those for 4lisefuliigh'frequency signals, respectively. In other Words,` high frequency noise, which isfgener'ally of llow "amplitude Will not be reproduced,Y but a signal having 'a `Iev`el "greater than the vilat portion of the input-'output characteristic, as shown in Fig. 3, will be reproduced. y

The mechanical system for discriminating against noise,v asfdeveloped in accordance With Vourpresentinvention,"can be applied to various types of sound translating devices. For the purpose 'of illustration, We have shovv'n our in- Vlitn applied lJ'O Athe Vibrating Systems 0f a 'dynamic' loudspeaker and a phonograph needle.

Fig. 7 illustrates Athe vibratingfsystem of an electro-dynamic loudspeaker 'constructed in ac- In order to discriminate against the il", I3, l connetei in series relation, with a groove I5 disposed in the connection be'tvveen the compliances. The groove l5 is substantially semicircular in cross section and has its concave portionfacinginvvardly. The initial compliance Il has itslfree end UI attached to an integral extension I9 'of the voice coil form, and the second comp I3 has' its free end 20 attached to the diaphragm l.y

, The extension la oi the voice coil 3 constitutes anon-linear driving element and has its free end 2l Aegtending outwardly and at substantially a right angle to the axis of the voice coil 3. The free 'eifi'd 2l is also suspended for movement Within the groove l5 so that the sides of the groove will ruiic'iioii as stops io limit the of'- fective compliance ofv the Ainitial compliance f I I. Thedis'tancebetl'veei the sides of the groove i5 is octcriiiiric'o according to the signal ampliiiioi'e above which the high frequency vsignals are desired to be reproduced. "In practice, when highA frequency signal's'are introduced into the syste-fh, the iv/,orco coil transmits them to the initial compliance l l and the `non#linear driving 'eieiii'eiit 'of nach oh jig. If the signals are.

below the soloctoo'hiii "ooe they will loo alosorbed the initialk hpliance III. 'n the other heno, iiihoh the signals ejif'ce'eoiihc predetermined amplitude, -che eno 2| of 'the rionlii'iooifeleipnt will 'strike the sioesof the 'groove I 5. Thereafter the fdriving"action becom'esline'ar and the useful-hi hifjrequenc'yr signals will be transmitted 'through tho second compliance la to the diaphragm for nrlal reproduction by 'the diaphragm.-

In Figs. life-nifl there is shown a vphonograph hoed-io op y-iiiseg oohsiriioioo in accoroaricov'vith our invention. The needle?? is providedvfi'th la reoor'o engaging poiliioh 2a; onoasharik 2`5 iiihich riiiiyl he ihscito ini-"o the rsocket 'or 'the like 'of a translating device in a mannerfvvell known in the art'. 'engaging portion 'and 'the'shank 'are connected b'y Vapa'ii" fofi compliancesl, 2li, 'dispo-seo ih' 'serios relation. 4A nongiiiieo'rorivih'g `clermont -fsii coiiipiilsiig two 'arms 3|, 3'3l isotta'clied to vthe `stylus 22 on opposite sides of the cor'iriec'tion between the compliancejs i21, 29;', 'Ihe 'arms are Vsupported in spaced, parallel'frie- Ila't'l'on toA theA record engaging portion 2'3fand have vtheir 'ends 35, 3-7 entendirigfninw'ardly Jtowards 'the v'record engagingportin.' The'ends'35, Sliterifninatfin closely spaced `relation to vthe record eni- 'gag'ingportion,` the spacing beingdependent'upon th'e desirdsigna-l amplitude range 'in 'the high frequoii'cyi iig iolooirohsinitioo bythe-hoodie 2'2' to'tl'1e translatln device.

Y Fig. Alo vshows afmooiiieofomfof phonograph necvol'il'i oori'striic' lin aco'oroance-fw'ith-our iiivoniioii. ,Tho :oo hoodie is similar Vto fthe needle f2y2 shot/ii irifFigs. v8 and 9, and incluoesfa rec-oro eiigagiiigipoi-i-ioh afsjhohkfaofa poirfo'f complionojs im, "a9 which are -oliposeo -iiifseie's relation `l'ietvveen ythe recel 'engaging-portionand ihefsliahh; ariofo nonlinear ldrivin'gfole'rhenifu consisting'ofttvo'armsl 53. The-arms 5'l,-'53 have orio of their Achos. 'oiia'cheofio 'the/connection`f54 betweenthe' complia-nces 41,fl9-'fan1 their opposite `ends F5 5; 51 Adisposed in` spaced ii'elation tothe Vrecord iengaging portion 43 in the same manner as in `the modification shown in Figs. 8

and 9. For `convenience of manufacture, however;.therecord engaging portion .43 and the compliance 41 are made separate from the shank 45, the compliance 43 and the connection 54. For the purpose of assembly, the vportion 43 is pro- .vided with an end 58 which is securely fastened in an aperture Si! in the connection 54.

engaging complementary threaded apertures 6l',

69 in the connection 54. The screws are provided with knurled heads 1I, T3 which are disposed on the free ends of the shanks 53, 65 and which bear against the external faces 15, 11 of the arms 5i, 53, while the threaded shanks eX- tend through apertures 13, 8l in the arms.

The phonograph needle shown in Figs. 8 and 9, and that shown in Fig. 10 operate fundamentally in the same way. -The initial compliances 27, 4l absorb or filter out all high frequency signals below a given amplitude. When high frequency signals above the predetermined amplitude are picked upV by the needle, the record engaging portions 23, d3 will strike the ends 35, 31, 55, 5i of Ythe non-linear driving elements 3D, 50. The vilar form of our invention described herein be considered as illustrative and not as limiting. What is claimed is: l. In signal translating apparatus, a vibrating `system for discriminating against undesirable signals comprising a driving member supported for vibratory movement in response to an eX- ternal driving force acting upon said driving member, translating means for translating the vibratory movements of said driving member, at least two compliances connecting said driving member to said translating means, said compliances being connected in series, and shunting means associated with said driving member for selectively shunting one of said compliances for i .selected signals.

`2. The invention set forth in claim l characterizedv in that said one compliance is adjacent said driving member, 'and characterized further in that said shunting means comprises a nonlinear driving element operatively connected to said driving member and said one compliance for transmitting high frequency signals beyond a predetermined amplitude.

3. The invention set forth in claim 2 further characterized inV that the connection between ,i said compliances includes limiting means, and characterized still further in that said non-linear drivingelement has one of its ends connected @Masai to said driving member and has its opPsite end freely suspended and operatively associated with said limiting means.V

4. The invention set forth in claim 3 further characterizedin that said limitingmeans comprises aV p air'of stops which are spaced apart a predetermined distance in accordance with the amplitude of the desired signals tobe reproduced.

5. Ihe invention set forthin claim 3 further characterized in that said non-linear driving element has means for varying the effectiveness of said one compliance. l

6. In signal translating apparatus, a vibrating system for discriminating against undesirable signals comprising an input driving element, a translating element for translating signals receivedbysaid input driving element, a plurality of compliances connecting said input driving element and said translating element, said compliances being connected in series, and an. intermediate driving element responsive to predetermined movements of said input driving element for selectively shunting one of said compliances for selected signals.

7. The invention set forth in claim 6 characterized in that the connection between said compliances includes limiting means, and characterized still further in that said intermediate driving i element has one of its ends attached tosaid input driving element, and the other of its ends freely suspended and operatively associated with said limiting means. i i

8. The invention set forth in claim 7 characterized in that said limiting means comprises a pair of stops separated by a predetermined distance whereby only vibrations above a predetermined amplitude will be transmitted to said translating element.

9. In a loudspeaker having a magnetic field structure, a vibrating system for discriminating against undesirable signals, said system comprising a voice coil, a diaphragm, at least two compliances connecting said diaphragm to said voice coil, said compliances being connected in series for transmitting vibratory motion from said voice coil to said diaphragm, and shunting means associated with said system for selectively shunting one of said compliances for selected signals.

10. The invention set forth in claim 9 characterized in that said shunting means comprises a non-linear driving element connected to said voice coil and operatively associated with that one of said compliant couplings which. is adjacent said voice coil.

11. The invention set forth in claim 10 further characterized in that the connection between said compliances includes limiting means, and characterized still further in that said non-linear driving element has one of its ends attached to said voice coil, and has its other end freely suspended and operatively associated with said limiting means.

, 12. The inventionset forth nfclaim 11| still further characterized in that said limiting means` comprises a groove disposed in said connection between said compliances within which said free end of said non-linear driving elementis suspended.

13. A stylus for sound reproducing machines comprising a shank portion, a. record engaging portion, a pair of series connected compliances connecting said shank portion to said record engaging portion, and shunting means associated with one of said compliances for selectively shunting said one compliance.

f necftion betvveensaidVr cornpliarmesV and having their opposite ends freely suspended in predetermined=spaoedrelatien te said recordengaging 1 portion.

16. The invention set forth in claim 15 characterized in that said non-linear driving element is provided with means for adjusting the distance between said freely suspended ends of said arms and said record engaging portion.

HARRY F. GLSON. JOHN ERESTON. Y

References cited in the me Qf this vpatent UNITED STATES PATENTS Number Number Name Date Fitzpatrick Apr. 28, 1908 Allwood Feb'. 21, 1911 Steinert Sept. 24, 1912 Ringel Judy 9, 1935 Rayment May 23, 193.9 Barker July 4, 1939v lSteers Mar. 8, 1941 Hewitt June 18, 1946 FOREIGN PATENTS Country Date Italy Jan. 5, 1940 Great Britain May 10, 1937 Great Britain Nov. 24,1948 

